(1) Field of the Invention
The invention relates to a photographic vesicular imaging composition, element and process. In particular, it concerns such an imaging composition and element containing radiation-sensitive vesiculating agents which imagewise decompose to form microscopic light-scattering vesicles of gas, usually within an appropriate binder. A spectral sensitizer can be used to extend the range of responsiveness.
(2) State of the Prior Art
Vesicular films are of considerable importance in information storage and retrieval, such as by microfilming, due to the facts that vesicular images have very high resulution and are extremely stable in ambient light and normal use temperatures. One of the most common classes of vesiculating agents is diazonium salts which, upon exposure to activating radiation, release nitrogen gas. By an appropriate selection of the binder, the gas is retained within the element until development by heat causes expansion of the gas into light-scattering vesicles. Typical examples are shown in U.S. Pat. Nos. 3,032,414 and 3,355,295 wherein it is noted that the binder should have a "permeability constant", which is in reality an impermeability constant, of between about 1 .times. 10.sup.-11 and 1 .times. 10.sup.-15 measured as the number of cubic centimeters of gas transmitted by 1 sq. cm. of the binder during 1 second at 30.degree. C. when the pressure gradient is 1 centimeter of Hg per cm of the thickness of the binder layer. Typical of patents disclosing vesiculating elements of this type are U.S. Pat. Nos. 2,699,392; 2,703,756; 2,923,703; 3,032,414; 3,208,850; 3,383,213; 3,620,743; and 3,622,335; and British Pat. No. 402,737 filed Mar. 4, 1932.
One of the more conspicuous problems of vesicular imaging has been the lack of a system which permits spectral sensitization of the vesiculating agent. Such lack is particularly noteworthy at a time when photographic silver halide materials have well-developed techniques for spectral sensitization, and even diazo-coupler dye materials are being spectrally sensitized as discussed hereafter. The result of such a lack is, of course, a limitation of the spectral response of the vesiculating element to that of the particular vesiculating agent used. The sensitivity of such agents is generally in the ultraviolet or near UV portions of the spectrum. UV sources are difficult to obtain, and furthermore interposition of any material which has a filtering effect on UV light reduces the sensitivity of such vesiculating agents to the point of rendering them less desirable for practical purposes. A filtering effect can result from the preparation of vesicular prints from negatives coated on polyethylene terephthalate film base due to the intensive absorption of light at certain short wavelengths by this film base material.
Diazonium compounds have been rendered photolytically responsive to radiation of wavelengths longer than their inherent sensitivity. However, in most such cases, this has been limited to solutions only, a process not having any practical use. Also diazo compounds are thermally unstable at elevated temperatures, which limits the temperature range available for film drying and processing.
Azides and bisazides have been spectrally sensitized by aromatic nitro derivatives, such as nitropyrenes, albeit not in a vesiculating imaging element, as described in F. Lewis and W. Saunders, J. of Amer. Chem. Soc., Vol. 90, page 7033, December 1968; and T. Tsunoda et al, Photog. Sci. and Eng., Vol. 17, No. 4, page 390 (July/August 1973).
A clear and continuing need has existed for a vesicular imaging composition and element that will permit improved spectral sensitization. None of the described patents or other references offer a suitable answer to this need.
Types of vesiculating agents other than those producing N.sub.2 have been noted in the art, including carbon monoxide releasing elements, ferric ammonium citrate, and even polyketones which apparently produce vaporizable monomers, Kosar, Light-Sensitive Systems, page 278 (1965); and U.S. Pat. No. 3,091,532. These, however, have not been disclosed as being spectrally sensitizable and have not used cyclopropenones specifically. Other examples of carbon monoxide releasing agents are disclosed in U.S. Pat. Nos. 1,944,293; 1,990,925; 1,976,302; and 1,919,194. Patents relating to cyclopropenones per se and methods of making them for use other than as vesiculating agents include U.S. Pat. Nos. 3,657,348; 3,782,938; and 3,787,500.